Semiconductor controlled safety time delay relay

ABSTRACT

A solid-state circuit is described for controlling a railroad signal delay device wherein the time element is formed by a capacitor and a resistor. A polarized relay is employed in a discharge circuit formed by the capacitor, a semiconductor switch and the coil of the relay. Expiration of the time element operates to close the switch in the discharge circuit. The coil of the relay is so oriented in the circuit that during capacitor charging, the magnetic bias is effectively increased, whereas during the discharge initiated by the closing of the semiconductor switch, the bias is overcome.

United States Patent lnventor Arthur E. Dodd Port Washington, N.Y.

Appl. No. 738,445

Filed June 20, 1968 Patented Feb. 9, 1971 Assignee Servo Corporation ofAmerica Hicksville, N.Y.

a corporation of New York SEMICONDUCTOR CONTROLLED SAFETY TIME DELAYRELAY Primary Examiner.lames D. Trammell Attorney-Kane, Dalsimer, Kane,Sullivan and Kurucz ABSTRACT: A solid-state circuit is described forcontrolling a railroad signal delay device wherein the time element isformed by a capacitor and a resistor. A polarized relay is employed in adischarge circuit formed by the capacitor, a semiconductor switch andthe coil of the relay. Expiration of the time element operates to closethe switch in the discharge circuit. The coil of the relay is sooriented in the circuit that during capacitor charging, the magneticbias is effectively increased, whereas during the discharge initiated bythe closing of the semiconductor switch, the bias is overcome.

I l /4 l ii I 'l I Q: s

' SEMICONDUCTOR CONTROLLED SAFETY TIME DELAY RELAY This inventionrelates to railway signal delay devices-More specifically, it relates toa railway safety relay wherein a delay, the time element, is obtainedelectronically, utilizing a semiconductor switch.

Railway applications of signal delay devices often require a wide rangeof delay times, say from a matter of seconds to minutes. Theconventional delay devices which establish the time element in responseto an external switch signal involve electromechanical arrangements suchas a pulse oscillator of selected pulse repetition rate driving astepping motor or a constant speed motor driving the contacts of aswitch towards a closed position in a selected time. In botharrangements, a clutch is employed to engage the motors and actuate thetime elements as well as quickly disengage the motors when the externalswitch signal is removed.

Accordingly it is an object of this invention to provide an improvedrailway signal delay device utilizing semiconductor circuitry having aminumum of moving parts, reduced maintenance and lower manufacturingcosts.

An important feature of a signal delay device as employed in railwaysignalling is that the failure of any component in the device should notcause a reduction in the delay or a premature pickup of the contactscontrolled by the delay device. Any failure should rather cause thedevice to either fail altogether or prolong the delay.

For instance, assume a track block is controlled by a pair of spacedlights which are timed to turn sequentially green after a preselectedinterval. if the interval is set for a train travelling at 30 miles perhour, then any shortening of the interval will not be noticed for acorrespondingly faster-travelling train. On the other hand, if theinterval is lengthened,then a faster train cannot pass the block undergreen light conditions.

Accordingly it is an object of my invention to provide a solid statesignal delay device having a minimum amount of components, a high degreeof reliability and which is essentially fail-safe in nature.

These objects are accomplished by my invention which is described asfollows in conjunction with the drawing which illustrates a schematicrepresentation of the circuitry used in the invention.

Briefly stated, my invention provides the time element with a capacitorcharging circuit, the charging circuit controls a polarized relay byincluding the coil of the relay in a discharge circuit composed of thecapacitor of the charging circuit and a semiconductor switch. The relayis magnetically biased and its coil is so oriented in the dischargecircuit that discharge currents produce magnetic flux in a directionwhich overcomes the magnetic bias and thus energizes the relay.

An external contact is operated by a train travelling along atrack orother suitable control means and is normally open but, when activated bythe passage of a train, closes to supply a DC voltage to the inputterminals of the signal delay device 13. The delay device 13 includes arelay controlling normally open contacts 28 which are to be closed foroperation in a railroad signalling circuit (not shown) upon elapse of apreselected time.

Within the signal delay device 13 a Zener diode 18 is coupled to theterminal 17 and through resistor 12 to terminal 17 to provide aregulated supply voltage to the circuitry. A charging circuit isestablished across the input terminals by the series connection of acapacitor 20, the coil 22 of a polarized relay and a variable resistor24.

In parallel with the capacitor 20 and the coil 22 is a siliconcontrolledswitch 30 having its anode tenninal 32 connected to the input terminal14, and its cathode terminal 36 connected to the common junction betweenthe coil 22 and the variable resistor 24. The cathode gate or triggerterminal 34 of the silicon-controlled switch 30 is connected to thecommon junction of two series-connected resistors 38 and 40 which arealso coupled across the input terminals and 17.

The polarizedrclay operates the controlcontacts 28 and is furtherprovided with a stick circuit including contact 26. The stick circuit iscoupled by line 42 to the common junction between the coil 22 and thecapacitor 20 and by line 44 to the input terminal 17. In parallel withthe coil 22 is a rectifier 23 having its anode coupled to the commonjunction between the coil 22 and the capacitor 20 and its cathodecoupled to the common junction formed between the coil 22 and thevariable resistor 24. This rectifier serves to reduce the voltagedeveloped across the coil when contact l0 is closed and may be dispensedwith when the switch can tolerate large anode to cathode potentials.

The polarized relay is of the so-called magnetic biased neutral type sothat, depending upon the orientation of the coil 22 within the circuit,the current through it will either increase the bias or overcome it. Inthe former case, the relay will not be energized, whereas in the latterthe relay will be activated to operate contacts 28. For the arrangementshown, the" direction of an arrow indicates the direction of currentflow in coil 22 to overcome the bias.

The operation of the circuit'is as follows. Upon the closing of theexternal contact 10, as caused by a train passing a given location, thefull terminal voltage is available across terminals 15 and 17. Since thecapacitor initially acts like a short circuit this terminal voltage iseffectively placed, at least initially, across the variable resistor 24.At the same time the cathode gate voltage relative to the cathode isnegative, so that the switch 30 cannot conduct and remains open.

As the capacitor 20 charges, the voltage across it increases and thevoltage across the resistor 24 decays. This renders the anode to cathodevoltage positive and changes the gate to cathode voltage to positiveafter some time delay; the measured time is a function of(2) a thresholddetermined by the voltage divider formed by resistors 38 and 40, as wellas (b) the time-constant of the RC network formed by capacitor 20 andresistor 24.

When the gate 34 becomes positive with respect to the cathode 36, thedesired time element has expired and the switch 30 is renderedconductive. This closes a discharge circuit formed by the capacitor 20,the switch 30 and the coil 22. Discharge of the capacitor 20, the switch30 and the coil 22 capacitor now takes place and a current is passedthrough the coil in the direction of the arrow, opposite to that of thecharging current, so that the relay is energized.

The operation of the relay closes the contact 26 of the stick circuit sothat as long as the external contact 10 supplies a DC voltage to thecircuit, a holding current will continue to flow through the switch 30,the coil 22 in the direction of the arrow, and the stick circuit.Opening of the external contact 10 will terminate the operation of therelay and return the contacts 28 to their open position.

Variable delays can be obtained by varying the resistance of thevariable resistor 24. Increase of the resistance increases the time forthe capacitor to charge and produces the desired longer delay. Also, theresistance 40 may be decreased to increase the time delay. 7

It can be seen that the breakdown of various elements in the circuitcannot cause premature picking up of the polarized relay. For instancethe breakdown of the capacitor 20, which may occasionally arise becauseof the large capacitance values needed for long time delays, rathercauses a flow of current in the direction that will cause an increase inthe bias of the relay coil, so that contacts 28 cannot be operated.

in the event of failure of switch 30, such as a short circuitingthereof, the shorting current will bypass the relay coil 22 and passthrough resistor 24 to the terminal 17.

The elimination of a clutch and a mechanical mechanism to establish atime element permits a significant reduction in the size of the deviceThe solid state time element can be placed in a single plug-in relaymodule space while earlier mechanical time element relays requiredseveral module spaces.

The preferred embodiment of this invention has been illustrated inconnection with a railroad switching application; the

invention, however, may be used in other fields where fail-safe featuresare important.

lclaim:

l. A signal delay device for controlling a railroad signalling circuitor the like with a magnetic biased relay having a stick circuit throughone of its sets of contacts and wherein an external contact supplies aDC signal through a pair of terminals to the delay device comprising: 7i

a charging circuit including in series connection across the pair ofterminals a capacitor, the coil of said relay and a time elementresistor, with the coil oriented in said charging circuit to produce anincrease in the bias of the relay from charging current flowing throughthe coil;

a discharge circuit including said capacitor, said coil and a normallyopen semiconductor switch arranged to discharge the capacitor throughthe coil, the discharge current being passed reversely through the coilin a direction to overcome the bias and energize the relay;

means responsive to the DC signal applied from the external contact andsaid terminals for generating a preselected control voltage for closingthe semiconductor switch at a preselected voltage level generated in thecharging circuit;

said stick circuit including the coil and the switch in seriesrelationship for passing current through the coil in a directioncontinuing to overcome the bias of the relay.

2. The device as recited in claim 1 wherein the switch-closing meansfurther comprises said semiconductor switch, said device having a pairof power terminals and a control gate terminal, with said powerterminals coupled across the coil and the capacitor, and a pair ofseries-connected resistors coupled across the DC signal terminals forproducing a reference voltage therebetween, with the control gateterminal coupled to the reference voltage for controlling the conductionof the semiconductor switch.

3. The device as recited in claim 1 and further including a bypassrectifier coupled across the coil in a direction for passing chargingcurrent around the coil and presenting a high impedance to dischargecurrents.

4. A signal delay device for controlling a railroad signalling circuitor the like with a relay wherein an external contact supplies a DCsignal through a pair of input terminals to the delay device,comprising:

a pair of resistors connected in series relationship across the pair ofinput terminals;

a semiconductor switching device including a trigger input coupled tothe junction between the resistors and having a pair of power terminals;

a capacitor and a time element resistor connected to form a time elementnetwork;

said relay being a magnetic biased relay having a coil for actuating therelay in response to current flowing in a first direction through thecoil and having plural sets of contacts, a stick circuit including oneof the sets of contacts, coupled across the coil to conduct currenttherethrough to one of the input terminals;

said capacitor and coil connected in series relationship across thepower terminals of the semiconductor switch with one of the powerterminals of the switch coupled to the other input terminal and theother power terminal coupled through the time element resistor to theone input terminal, said coil having a common junction with the timeelement resistor and the other power terminal, said coil being orientedto increase the bias in response to charging currents flowing throughthe capacitor and overcome the bias in response to discharge currentsfrom the capacitor.

1. A signal delay device for controlling a railroad signalling circuitor the like with a magnetic biased relay having a stick circuit throughone of its sets of contacts and wherein an external contact supplies aDC signal through a pair of terminals to the delay device comprising: acharging circuit including in series connection across the pair ofterminals a capacitor, the coil of said relay and a time elementresistor, with the coil oriented in said charging circuit to produce anincrease in the bias of the relay from charging current flowing throughthe coil; a discharge circuit including said capacitor, said coil and anormally open semiconductor switch arranged to discharge the capacitorthrough the coil, the discharge current being passed reversely throughthe coil in a direction to overcome the bias and energize the relay;means responsive to the DC signal applied from the external contact andsaid terminals for generating a preselected control voltage for closingthe semiconductor switch at a preselected voltage level generated in thecharging circuit; said stick circuit including the coil and the switchin series relationship for passing current through the coil in adirection continuing to overcome the bias of the relay.
 2. The device asrecited in claim 1 wherein the switch-closing means further comprisessaid semiconductor switch, said device having a pair of power terminalsand a control gate terminal, with said power terminals coupled acrossthe coil and the capacitor, and a pair of series-connected resistorscoupled across the DC signal terminals for producing a reference voltagetherebetween, with the control gate terminal coupled to the referencevoltage for controlling the conduction of the semiconductor switch. 3.The device as recited in claim 1 and further including a bypassrectifier coupled across the coil in a direction for passing chargingcurrent around the coil and presenting a high impedance to dischargecurrents.
 4. A signal delay device for controlling a railroad signallingcircuit or the like with a relay wherein an external contact supplies aDC signal through a pair of input terminals to the delay device,comprising: a pair of resistors connected in series relationship acrossthe pair of input terminals; a semiconductor switching device includinga trigger input coupled to the junction betweEn the resistors and havinga pair of power terminals; a capacitor and a time element resistorconnected to form a time element network; said relay being a magneticbiased relay having a coil for actuating the relay in response tocurrent flowing in a first direction through the coil and having pluralsets of contacts, a stick circuit including one of the sets of contacts,coupled across the coil to conduct current therethrough to one of theinput terminals; said capacitor and coil connected in seriesrelationship across the power terminals of the semiconductor switch withone of the power terminals of the switch coupled to the other inputterminal and the other power terminal coupled through the time elementresistor to the one input terminal, said coil having a common junctionwith the time element resistor and the other power terminal, said coilbeing oriented to increase the bias in response to charging currentsflowing through the capacitor and overcome the bias in response todischarge currents from the capacitor.